Optical systems for determining the geographical position of a source of light are used in a variety of applications. For example, conventional laser-guided missiles make use of reflected light from a laser beam pointed toward a potential target. Once a target is selected, information from the laser beam is used to determine the position of the target relative to the missile.
Such laser-guided missile systems are known in the art. One exemplary system is described in U.S. Pat. 5,784,156, to Nicholson, incorporated herein by reference. The incoming reflected light is detected at apertures located at different points on the exterior of the missile, typically on the nose cone or wing edges. Each aperture is provided with a lens or lens system that focuses the incoming light onto a bundle of fiber optic cables running inside the missile. The fiber bundles then transmit the incoming light onto sensors that convert the incoming light into electrical signals. These electrical signals are then analyzed by computers on board the missile to determine the relative distance, azimuth, and elevation between the missile and the object from which the incoming laser light is reflected.
Each aperture and its corresponding fiber bundle, or bundles, possesses a field-of-view (“FOV”), i.e., an angle from which it can detect light. All of the individual FOV of the apertures together form the overall FOV of the missile. Since the FOV of a given aperture is limited by the optics involved, to increase the FOV of a missile, one must typically increase the number of apertures and lenses employed by the missile. This problem is illustrated in FIG. 1B.
FIG. 1B shows a conventional dual lens “telescope” aperture configuration. In this configuration, the aperture is fitted with a primary lens 100 that focuses the incoming light rays, shown by dotted lines 102, onto a secondary lens 104. The secondary lens 104 then focuses incoming light rays onto a bundle of fiber optic cables 106. The fiber bundle 106 then transmits the incoming light onto sensors in the missile that convert the incoming light into electrical signals, which are used to determine the location of the target as discussed earlier. The FOV of the dual lens aperture arrangement shown in FIG. 1B is limited by the optical properties of the primary and secondary lens used. The FOVs are limited by off-axis light rays, and a typical FOV is plus or minus 10 or 15 degrees in conventional missile systems.
Similarly, another optical laser-guided missile system currently in use employs a plurality of ball lenses at each aperture, with each ball lens associated with a single fiber bundle. This arrangement is shown in FIG. 1 in which a ball lens 108 is used to focus incoming light rays 110 onto a fiber bundle 112. While this system is in some ways more advantageous than the dual lens system shown in FIG. 1B, it, nevertheless, still is limited to the FOV defined by the optical properties of the ball lens 108 and the fiber bundle 112. Increasing the FOV of the missile would still involve providing additional ball lens/fiber bundle arrangements in additional apertures located on the missile. For example, a conventional Hellfire IR seeking missile creates 32 FOVs by using 32 apertures mounted in two circumferential rings in the missile nose.